Why is it difficult to achieve profound anesthesia in inflamed tissues?

Achieving profound anesthesia in inflamed tissues is challenging primarily due to lower pH levels in the affected areas. Inflammation typically results in the accumulation of lactic acid and other metabolites that lower the pH of the tissue. Local anesthetics are weak bases and their effectiveness depends significantly on their ability to exist in a non-ionized (or unionized) form, which can easily penetrate nerve membranes.

At lower pH levels, there is a greater concentration of ionized form of the local anesthetic, which is less capable of diffusing through the nerve membrane. Consequently, this ionization reduces the overall efficacy of the local anesthetic, leading to inadequate analgesia or anesthesia in inflamed tissues. This phenomenon is particularly relevant in situations like dental procedures or surgical interventions, where inflammation can be present and complicate the anesthetic effect.

The other factors related to blood flow, pH, and proximity to nerves do influence the distribution and effectiveness of local anesthetics, but the critical issue in inflamed tissues is primarily the reduced pH, which directly affects the balance between ionized and non-ionized forms of the drug.